1. Field of the Invention
The invention relates to a shift control device for a vehicle and a control method therefor. More specifically, the invention relates to engagement force control for a friction engagement device in the shift control device at the time of an upshift.
2. Description of Related Art
An automatic transmission is widely used, in which a plurality of gear positions with different gear ratios are established according to engagement/release states of a plurality of friction engagement devices. The gear position of the automatic transmission can be automatically shifted according to a shift condition (a shift map or the like) set using parameters such as the amount of accelerator operation and the speed of a vehicle. For example, as shown in FIG. 6, the gear position can be shifted to a high speed side in which the gear ratio is low, as a vehicle speed V increases and as a throttle valve opening θTH (corresponding to the amount of accelerator operation) decreases. According to a related art of the invention, at the time of an upshift when a predetermined friction engagement device is engaged and the gear position is shifted to the high-speed side where the gear ratio is low, the engagement force of the friction engagement device is appropriately controlled to prevent a shift shock such as an abnormality, i.e., a sharp increase in revolutions of a drive power source, or to reduce the shifting time. For example, Japanese Patent Laid-Open Publication No. 10-331963 discloses an art in which an initial hydraulic pressure value (initial engagement force) at the start of shift is subjected to learning correction according to a change in an input revolution speed of an automatic transmission at an inertia-phase initial stage, and a hydraulic pressure preliminary fill time (backlash reducing time) is subjected to learning correction according to the time when an abnormality in revolutions of a drive power source has occurred.
However, even though the engagement force at the initial shift stage or the like is subjected to learning correction, there is a possibility that a shift shock such as a change in drive power may occur due to abrupt engagement at the completion of a shift, i.e., at the time when the friction engagement device is completely engaged.